In testing semiconductor devices and determining operating characteristic of the semiconductor device, test must be run on the device at various temperatures.
The semiconductor device is usually placed in a variable temperature controlled environment. The problem that exist is in accurately determining the device temperature, finding accurate temperature ovens that are easily movable and yet give accurate measurement of the temperature of the semiconductor device.
Even in currently available equipment, it is very costly to achieve and maintain a temperature of +/-1 degrees C. Achieving temperatures of +/-0.5 degree is even more costly.
Current methods blow air over electric coils. Dried air or dry nitrogen is blown through a freon evaporator for cold air. Cold air may also be obtained by injecting nitrogen into an air stream. To achieve uniform temperatures, the air must be uniformly directed on each device. This is difficult to do in a production environment.
Temperature calibration is required whenever a change in volume or direction of air flow is made.
In order to repair current temperature test chambers, it is necessary to bring the chamber to room temperature. After repair it takes time to bring the chamber back up to a stable temperature.
A further feature of the current temperature chambers is that air temperature is measured, not the temperature of the device.